A number of environmental carcinogens which include nitrosamines, pesticides and general carcinogens such as methylnitrosoureas cause marked depression of NAD levels in tissues and cells. We have shown that this NAD depression is accompanied in HeLa cells bya significant enhancement in poly (ADP-ribose) polymerase activity. This chromosomal enzyme utilizes NAD to synthesize poly (ADP-ribose) on various chromosomal proteins. The studies outlined in this application will examine the mechanisms underlying the influences of carcinogens on poly (ADP-ribose) polymerase at the basic unit of chromatin, the nucleosome. In addition, the program will investigate the interaction of selected carcinogens within precise regions of the nucleosomal structure of chromatin. The strategy of the program is to obtain this information in a systematic fashion, starting first at the simple mononucleosome level of chromatin, and ultimately progressing toward more complex forms of nucleosomes. Accordingly, we have 2 Specific Aims in this program: Specific Aim 1: Basic characteristics of the effect of MNU and poly (ADP-ribose) polymerase at the level of: 1. The nucleosome core particle plus or minus linker regions; 2. Simple nucleosome oligomers (2N, 4N); 3. Higher orders of chromatin complexity (2N yield 20N) especially at the level of nucleosomes 8-10 N where we find maximal activity for poly (ADP-ribose) polymerase in chromatin. Specific Aim 2: Molecular considerations for the binding of nitrosoureas to chromatin: 1. Carbamoylation and alkylation of the core and internucleosome regions of chromatin; 2. Alkylation of regions of chromatin of specific DNA base sequences; 3. Interaction with euchromatin and heterochromatin; 4. Interaction with the DNA replication regions of chromatin.